As disclosed in Patent Document 1, for example, the conventional rotary cutting tool is known as a rotary cutting tool in which a circular plate-like cutting insert is mounted on a sheet member attached to a tool body so as to rotate freely, thus performing cutting by allowing the cutting insert to be driven rotationally with the sheet member by a cutting resistance which acts on the cutting insert. Moreover, in the above-described rotary cutting tool, there is a case where the cutting insert does not rotate depending on the direction in which the cutting insert is fed to a work piece.
Further, when the cutting insert is mounted on the tool body so as to rotate freely with the sheet member, the sheet member is required to be attached to the tool body via a bearing, etc., which may pose a problem with durability, etc., of the sheet member. It is to be noted that, as a conventional clamping mechanism of the above-described circular plate-like cutting insert, Patent Document 1 has disclosed that which is described in Patent Document 2.
On the other hand, in recent years, a composite processing machine has been widely used in which a tool retaining portion of a lathe can be rotated to provide milling functions. According to the above-described composite processing machine, a work piece can be turned, while the circular plate-like cutting insert is driven rotationally around the central axis line thereof at a desired rotating speed, irrespective of the direction in which the work piece is fed. Further, no bearing, etc., for rotating the cutting insert is required to be mounted on the tool body.
Here, FIG. 17 and FIG. 18 embody a rotary cutting tool which is attached to the above-described composite processing machine and driven rotationally. In the thus embodied rotary cutting tool, the rear end portion of a tool body 1 which is made of steel, etc., and formed approximately in a cylindrical shape at the center of the axis line O is provided as a shank portion 1A which is attached to the composite processing machine, and the leading end portion of the tool body 1 is provided as a neck portion 1B. A circular plate-like cutting insert 3 is mounted on a recessed insert attachment seat 2 formed on the tip surface (leading end surface) of the neck portion 1B so as to be coaxial therewith.
This cutting insert 3 is made of a hard material such as cemented carbide, etc. In this example, the cutting insert 3 is a circular truncated cone-like positive insert which is formed so as to gradually decrease in the outer diameter of a peripheral surface as a flank 6 arranged between a rake face 4 and a seating surface 5 from a first circular side surface which serves as the rake face 4 to a second circular side surface which serves as the seating surface 5 opposite thereto. Then, a circular cutting edge 7 is formed at a ridge line portion where the rake face 4 intersects the flank 6, and a mounting hole 9 into which a clamping screw 8 for mounting the cutting insert 3 on the tool body 1 is inserted is penetrated and installed from the rake face 4 to the seating surface 5 along the central axis C of the cutting insert 3 to coincide with the above-described axis line O.
In this example, the neck portion 1B of the tool body 1 on which the above-described cutting insert 3 is mounted is formed in a tapered long circular truncated cone shape in such a manner that the rear end portion thereof is made smaller in diameter than the above-described shank portion 1A and slightly decreased in the outer diameter gradually as the rear end portion moves to the leading end side. Then, the above-described insert attachment seat 2 formed on the tip surface of the neck portion 1B is recessed so as to accommodate a part on the side of the seating surface 5 of the cutting insert 3.
That is, as shown in FIG. 18, the insert attachment seat 2 is constituted with an externally circular bottom surface 2A perpendicular to the axis line O on which the seating surface 5 is seated, facing toward the leading end side so as to be further recessed from the above-described tip surface, and a recessed conical surface-like wall surface 2B at the center of the axis line O which extends in an inclined manner so as to gradually increase in diameter according to an angle of the flank 6 with respect to the seating surface 5 to the leading end side from a periphery of the bottom surface 2A. Further, a threaded hole 2C into which the above-described clamping screw 8 is screwed is formed at the center of the bottom surface 2A along the axis line O.
The cutting insert 3 is seated on the thus formed insert attachment seat 2 in such a manner that the seating surface 5 is firmly attached to the bottom surface 2A and a part on the side of the seating surface 5 of the flank 6 is firmly attached to the wall surface 2B. And the clamping screw 8 which has been inserted into the above-described mounting hole 9 is screwed into the threaded hole 2C, by which the cutting insert 3 is pressed by a flat countersunk screw head-like head portion 8A of the clamping screw 8 and mounted at the leading end of the tool body 1. Further, in the tool body 1 on which the cutting insert 3 has been mounted, the shank portion 1A is retained by a tool retaining portion of the above-described composite processing machine and driven rotationally around the axis line O at a predetermined rotating speed. And the above-described cutting edge 7 cuts into a work piece, thereby turning the work piece.